Assuming you guys are comfortable making/modifying hubs, Harbor Freight has an option:
http://www.harborfreight.com/8-inch-...ire-47638.html
They are listed at 8", but are closer to 8.5" IIRC. There's a few Harbor Freight locations around Philadelphia (Sharon Hill, Norristown, Northeast Philly) if you want to inspect them in person.